Relation between algal available phosphate in the sediments of the River Garonne and chemically-determined phosphate fractions

Concentrations of total and inorganic phosphate were measured in forty-seven sediments of the River Garonne (France) using an anion resin, NaOH 0.1 M, Ca-NTA and Na-EDTA. Algal available P was measured using Scenedesmus crassus. The sediments presented a wide range of Tot-P concentrations (226 to 923 μg g⁻¹). Resin P varied between 1.1 to 55.5 μg g⁻¹ and NaOH-P between 3.5 to 262 μg g⁻¹. NTA-P and EDTA-P varied between 13.9 and 178 μg g⁻¹ and between 14.4 to 261 μg g⁻¹ respectively. Algal available P varied between 8.8 to 262 μg g⁻¹/ All forms of P are highly correlated and specially with algal available P (r = 0.70, 0.77, 0.88 and 0.77 for resin-P, NaOH-P, NTA-P and EDTA-P respectively). Nevertheless the partial correlation between EDTA-P and algal available P dropped to 0.05 when the concentration of NTA-P was considered as constant, indicating a spurious correlation with apatitic phosphate (extracted by Na-EDTA). Because of the strongest R ² and the lowest standard error of estimate, phosphate extracted by Ca-NTA can be considered as the best predictor of algal available phosphate.     

Nitrogen and phosphorus uptake by the Brazilian kelp Laminaria abyssalis (Phaeophyta) in culture

The uptake of ammonium, nitrate and phosphate by laboratory-grown young sporophytes of Laminaria abyssalis was measured in a perturbed system (batch mode) at 18 °C and 35 ± 5 µE m^–2 s^–1 photon flux density. Uptake of all appeared to follow saturation-type nutrient uptake kinetics. The NO _inf3 ^sup– (K _s = 14.0 µM, V _max = 5.0 µmol h^–1 g^–1 dry wt) and NH _inf4 ^sup+ (K _s = 4.6 µM, V _max= 2.0 µmol h^–1 g^–1 dry wt) were taken up simultaneously, although NH _inf4 ^sup+ was taken up more rapidly. Values of K ₃ and V _max for phosphate were, respectively, 2.21 µM and 0.83 µmol h^–1 g^–1 dry wt. Nitrate and phosphate were both consumed in similar rates (V _max /Ks 0.37) at low concentrations. NH _inf4 ^sup+ , thus, might be a more efficient form of N fertilizer if artificial enrichment of seawater is used.     

Carbohydrate metabolism in one- and two-year-old spruce needles, and stem carbohydrates from three months before until three months after bud break

Starch and sucrose metabolism of one- and two-year-old needles of Norway spruce (Picea abies [L.] Karst., about 30 years old) was investigated from three months before until three months after bud break at a natural site. We distinguish different metabolic states according to the extractable activities of enzymes (α-amylase [EC 3.2.1.1], ADP-glucose pyrophosphorylase [AGP, EC 2.7.7.27], D-enzyme [EC 2.4.1.25], starch phosphorylase [STP. EC 2.4.1.1]), sucrose phosphate synthase [SPS, EC 2.4.1.14], sucrose syntbase [SS, EC 2.4.1.13]. acid invertase [AI, EC 3.2.1.261) and pool sizes of related metabolites (starch, glucose, fructose, sucrose, raffinose, stachyose, fructose 6-phosphate [F6P], glucose 6-phosphate [G6P], fructose 2,6-bisphosphate [F26BP], and inorganic phosphate [P₁]). The period ending with bud break was characterized by high rates of net photosynthesis, a pronounced decrease in the amount of soluble sugars, and a steep rise in starch (from the detection limit to approximately 600 nmol glycosyl units [mg dry weight]_-1). In parallel, the extractable activity of AGP increased, while D-enzyme was on a relative high level when compared with the period after bud break. With respect to sucrose metabolism, F26BP, an inhibitor of sucrose synthesis, decreased from 1 to 0.4 pmol (mg dry weight)_-1. This was complemented by SPS activity, which was due to both increased protein levels shown by immunoblotting and activation under metabolite control (high levels of G6P and a low P_i/G6P ratio). This indicates a high capacity of synthesis of starch and sucrose in the period before bud break. These observations are in accordance with estimates of photosynthetic carbon gain, which indicate that in early spring large amounts of carbon from current photosynthesis are exported out of the needles. In addition, the content of nonstructural carbohydrates (expressed as hexoses) increased in the bark of the stem. This could also be a consequence of an enhanced carbon export from the needles. After the onset of bud break, starch concentration decreased in all tissues under investigation. In contrast, the level of total nonstructural carbohydrates in the outermost sapwood nearly doubled from bud break until the end of sampling. In the needles, net photosynthesis was reduced by about 75% and a decrease in SPS activity and protein level were found together with lower G6P concentration, and an increased P_i/G6P ratio. These results suggest that during that period sucrose synthesis was reduced in the older needles. In addition, under conditions of reduced photosynthesis, carbon demand of current year needles was in part ensured by the mobilization of starch in the older needles. Taken together our data show that before bud break carbon metabolism of mature leaves is related with the sink demands of storage organs. After bud break the accumulated assimilate pools in needles and stem, mainly the bark, are mobilized and support carbon supply to new tissues.     

Sucrose accumulation in sweet sorghum stem internodes in relation to growth

Sweet sorghum (Sorghum bicolor L. Moench) stems of different cultivars (NK 405. Keller and Tracy) reveal a different pattern of sucrose accumulation with respect to in-ternodal sugar content and distribution. The onset of sucrose storage is not necessarily associated with the reproductive stage of the plant, as was hitherto assumed, but obviously occurs after cessation of internodai elongation as was postulated for the sugarcane stem. For at least two of the three cultivars, ripening is an internode to internode process beginning at the lowermost culm parts. Intensive growth of the internodes, combined with a high hexose content in stern parenchyma, shows a strong positive correlation (r |Mg 0.94) to the activity of sucrose synthase (SuSy; EC 2.4.13), but not to invertase (EC 3.2.1.26) which is not present as soluble (neutral and acid) or cell wall-bound, salt-extractable enzyme in the three culsivars investigated. Sucrose synthase measured in sucrose cleavage and synthesis direction reveals divergent activity rates and sensitivity towards exogenously applied Mg²⁺ ions and pH. SuSy activity is connected to the increase of internodai sucrose content in so far as (1) its decline is a prerequisite for the onset of sucrose accumulation and (2) it remains at a constant low level during sucrose storage. Sucrose phosphate synthase (SPS; EC 2.4.1.14) activity in the sorghum stem is low compared to SuSy and uniformly distributed over all inter-nodes. Only source leaves of sorghum show a considerable SPS activity, but neither stem nor leaf SPS reveal a positive correlation to the increase of internodai sucrose content. Sucrose phosphate phosphatase (SPP; EC 3.1.3.24) amounts lo only 24–30% of the respective SPS activity but follows the same distribution pattern. None of the enzymes under study proves to be responsible for the extent of sucrose storage in the stem, so other phenomena such as transport processes within the stern tissue require further investigation.     

Effect of intermittent CO2 enrichment during nutrient starvation on tertiary treatment of wastewater by alginate-immobilized Scenedesmus bicellularis

A method of accelerating the removal of ammonium and phosphate by the unicellular microalga Scenedesmus bicellularis is presented for municipal tertiary wastewater treatment using immobilized cells to obtain a high quality of effluents. Microalgal cells grown in defined medium were harvested by centrifugation and stored at 4°C in the dark for 8 months before immobilization. The concentrated cell suspension was then immobilized in alginate films supported on polypropylene screens. Immobilized cells were incubated in a water-saturated air stream enriched with CO₂ at 750, 1,000, or 1,500 ppm for 3 h periods followed by 2 h periods without enrichment. The quantitative effects of these three CO₂ enrichments on nutrient uptake from secondary municipal wastewater effluent were compared to a control laboratory air at 320 ppm under the same conditions of illumination, photoperiod, and humidity. The exposure cycle of 48-h nutrient deprivation in air with CO₂ enrichment followed by 2 h of nutrient uptake from wastewater was repeated three times with a residual NH₄---N content dropping to 0% after 105 min for the 1,500 ppm CO₂ treatment and to 34% of the initial level after 120 min for the control treatment. Complete PO₄---P removal required more than 2 h. The chlorophyll a contents obtained with 1,000 and 1,500 ppm CO₂ enrichments were comparable. This study establishes that intermittent CO₂ enrichment during nutrient deprivation of immobilized microalgal cells in a water-saturated air stream may accelerate tertiary wastewater treatment.     

Importance of mitochondrial transmembrane processes in human mitochondriopathies

In a substantial group of subjects suspected to have a mitochondriopathy no defect in the mitochondrial energy metabolism (pyruvate dehydrogenase complex or respiratory chain complexes) can be demonstrated. At least in some of these subjects it seems justified to consider a defect in one of the proteins which mediate the transport of several ions and substrates across the mitochondrial membranes. Of particular interest are proteins which are directly involved in the process of oxidative phosphorylation, such as the adenine nucleotide translocator (ANT) and the phosphate carrier (PiC). However, defects in transmembrane ion transporters also may induce impaired energy metabolism probably as a result of osmotic disturbances within the mitochondrial matrix. In this respect, the voltage-dependent anion channel (VDAC) and other ion channels have to be taken into consideration. Here we review the still incomplete knowledge of the occurrence of ANT, PiC, VDAC, cation channels, and a few substrate carriers in human tissues, as well as their possible role in pathology.     

Active site model for gamma-aminobutyrate aminotransferase explains substrate specificity and inhibitor reactivities.

A homology model for the pig isozyme of the pyridoxal phosphate-dependent enzyme gamma-aminobutyrate (GABA) aminotransferase has been built based mainly on the structure of dialkylglycine decarboxylase and on a multiple sequence alignment of 28 evolutionarily related enzymes. The proposed active site structure is presented and analyzed. Hypothetical structures for external aldimine intermediates explain several characteristics of the enzyme. In the GABA external aldimine model, the pro-S proton at C4 of GABA, which abstracted in the 1,3-azaallylic rearrangement interconverting the aldimine and ketimine intermediates, is oriented perpendicular to the plane of the pyridoxal phosphate ring. Lys 329 is in close proximity and is probably the general base catalyst for the proton transfer reaction. The carboxylate group of GABA interacts with Arg 192 and Lys 203, which determine the specificity of the enzyme for monocarboxylic omega-amino acids such as GABA. In the proposed structure for the L-glutamate external aldimine, the alpha-carboxylate interacts with Arg 445. Glu 265 is proposed to interact with this same arginine in the GABA external aldimine, enabling the enzyme to act on omega-amino acids in one half-reaction and on alpha-amino acids in the other. The reactivities of inhibitors are well explained by the proposed active site structure. The R and S isomers of beta-substituted phenyl and p-chlorophenyl GABA would bind in very different modes due to differential steric interactions, with the reactive S isomer leaving the orientation of the GABA moiety relatively unperturbed compared to that of the natural substrate. In our model, only the reactive S isomer of the mechanism-based inhibitor vinyl-GABA, an effective anti-epileptic drug known clinically as Vigabatrin, would orient the scissile C4-H bond perpendicular to the coenzyme ring plane and present the proton to Lys 329, the proposed general base catalyst of the reaction. The R isomer would direct the vinyl group toward Lys 329 and the C4-H bond toward Arg 445. The active site model presented provides a basis for site-directed mutagenesis and drug design experiments.     

The mobile ferrous iron pool in Escherichia coli is bound to a phosphorylated sugar derivative

Based on in vivo Mössbauer spectroscopy it has previously been demonstrated that the intracellular iron pool of Escherichia coli, grown in iron deficient media supplemented with siderophores as the sole iron source, is dominated by a single Fe²⁺ and a single Fe³⁺ species. We have isolated the ferrous ion species and have purified it employing native column PAGE, chromatography and ultrafiltration. The purified compound displays an M _app of 2.2 kDa and an extremely low isoelectric point (pI) of 1.05. It is shown that this ferrous ion binding compound is neither a protein nor a nucleotide, rather it is composed mainly of phosphorylated sugar derivatives. This compound binds approximately 40% of the cytoplasmic iron. Therefore it is proposed that this oligomeric ferrous carbohydrate phosphate represents the long sought after mobile, low molecular mass iron pool.     

A model of the pentose phosphate pathway in rat liver cells

A mathematical model based on kinetic data taken from the literature is presented for the pentose phosphate pathway in fasted rat liver steady-state. Since the oxidative and non oxidative pentose phosphate pathway can act independently, the complete (oxidative + non oxidative) and the non oxidative pentose pathway were simulated.Sensitivity analyses are reported which show that the fluxes are mainly regulated by D-glucose-6-phosphate dehydrogenase (for the oxidative pathway) and by transketolase (for the non oxidative pathway). The most influent metabolites were the group ATP, ADP, P₁ and the group NADPH, NADP⁺ (for the non oxidative pathway).Abbreviations GK Glucokinase, (E.C. 2.7.1.2.) - G6PDH D-glucose-6-phosphate dehydrogenase, (E.C. 1.1.1.49) - PLase 6-Phosphogluconelactonase, (E.C. 3.1.1.31.) - PGIcDH 6-Phosphogluconate dehydrogenase, (E.C. 1.1.1.44) - RPI D-ribose-5-phosphate keto-isomerase, (E.C. 5.3.1.6) - TK D-sedoheptulose-7-phosphate: D-glyceraldehyde-3-phosphate glycol-aldehyde transferase, (E.C. 2.2.1.1.) - TA D-sedoheptulose-7-phosphate: D-glyceraldehyde-3-phosphate dihydroxyacetone transferase, (E.C. 2.2.1.2) - EP D-ribulose-5-phosphate-3-epimerase, (E.C. 5.1.3.1) - PGI D-glucose-6-phosphate keto-isomerase, (E.C. 5.3.1.9) - TPI D-glyceraldehyde-3-phosphate keto-isomerase, (E.C.5.3.1.1)     

Response of the rat heart to catecholamines and thyroid hormones

Catecholamines and thyroid hormones have a similar influence on heart function and metabolism, but this may occur in a differential manner and to a different extent In this study, the effects of norepinephrine (NE) and of triiodothyronine (T₃) were studied in regard to the function of the left (LV) and right ventricle (RV) and to the oxidative pentose phosphate pathway (PPP). NE was applied in rats as continuous i. v. infusion (0.2 mg/kg/h) for three days. T₃ was given as daily s.c. injections (0.2 mg/kg) for the same period of time. LV, and RV function was measured in the closed-chest trapanal-anesthetized animals using special Millar ultraminature catheter pressure transducers. NE induced an increase in heart rate, in mean arterial pressure, and in total peripheral resistance (TPR). The cardiac RNA/DNA and the left ventricular weight/body weight ratios were increased by about 40%. These effects were prevented by simultaneous -and -receptor blockade with prazosin and metoprolol, respectively, but not by verapamil which abolished the hemodynamic effects. RVSP was significantly elevated by NE in a dose-dependent manner. The functional effects of T₃ on the LV were not as pronounced as those induced by NE. Heart rate and LV dp/dt_max were increased by T₃ and this increase was prevented by concomitant -receptor blockade with, metoprolol. In contrast to NE, T₃ induced an increase in cardiac output and a concominant decrease in TPR. The RNA/DNA ratio was elevated and cardiac hypertrophy had developed after treatment for three days with T₃. These changes were not affected by -receptor blockade with metoprolol. RVSP was increased by T₃ to a lesser extent than with NE. In metabolic terms in turned out that only NE, but not T₃ had a stimulating effect on the cardiac PPP. NE increased the mRNA and activity of glucose-6-phosphate dehydrogenase (G-6-PD), the first and regulating enzyme of this pathway. However, there was no effect of T₃ on G-6-PD activity nor on 6-phosphogluconate dehydrogenase activity, one of the following enzymes in the pathway within the first 5 days of T₃ treatment. These results demonstrate that the functional effects of T₃ were not as pronounced as or even different from those of NE, and that T₃ lacked a stimulating effect on the cardiac PPP.